C3 carbon fixation is one of three metabolic pathways for carbon fixation in photosynthesis, along with C4 and CAM.
In the C3 process carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) are converted into 3-phosphoglycerate through the following reaction:CO2+RuBP→(2)3-phosphoglycerate.
The C3 plants, originating during Mesozoic and Paleozoic eras, predate the C4 plants and still represent approximately 95% of Earth's plant biomass. C3 plants lose 97% of the water taken up through their roots to transpiration
Plants that survive solely on C3 fixation (C3 plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and ground water is plentiful.
Examples for C3-plants include rice, wheat, orange tree, wine plant, coffee plant, tobacco plant, tea plant, peanut plant, lemon tree, potato, carrot, tomato, peach tree, apple tree, pear tree, mango tree and barley.
Further examples include oats, rye, triticale, dry bean, soybean, mung bean, faba bean, cowpea, common pea, chickpea, pigeon pea, lentil, banana, coconut, taro, yams, sweet potato, cassava, sugar beet, cotton, jute, sisal, sesame, sunflower, rapeseed and safflower.
C3 plants have disadvantages to grow in hot areas because the enzyme Ribulose-1,5-bisphosphate-carboxylase/-oxygenase (RuBisCO) incorporates more oxygen into RuBP as temperature increases. This leads to increased photorespiration, which leads to a net loss of carbon and nitrogen from the plant and can, therefore, limit growth. In dry areas, C3 plants shut their stomata to reduce water loss, but this stops CO2 from entering the leaves and, therefore, reduces the concentrating of CO2 in the leaves. This lowers the CO2:O2 ratio and, therefore, also increases photorespiration.
C4 and CAM plants, on the other side, have adaptations that allow them to survive in hot and dry areas, and they can, therefore, out-compete C3 plants.
C4 carbon fixation is one of three biochemical mechanisms, along with C3 and CAM photosynthesis, used in carbon fixation. It is named for the 4-carbon molecule present in the first product of carbon fixation in the small subset of plants known as C4 plants, in contrast to the 3-carbon molecule products in C3 plants.
C4 fixation is an elaboration of the more common C3 carbon fixation and is believed to have evolved more recently. C4 and CAM overcome the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in what is called photorespiration. This is achieved by using a more efficient enzyme to fix CO2 in mesophyll cells and shuttling this fixed carbon via malate or aspartate to bundle-sheath cells. In these bundle-sheath cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO2 released by decarboxylation of the malate or oxaloacetate. These additional steps, however, require more energy in the form of ATP. Because of this extra energy requirement, C4 plants are able to more efficiently fix carbon in only certain conditions, with the more common C3 pathway being more efficient in other conditions.
However, also C4 can be modified according to the present invention in order to improve the carbon fixation even further.
Examples for C4 plants include crab grass, corn (maize), amaranth, sorgham, millet, sugarcane, nut grass, crab grass, barnyard grass, fourwinged salt bush and chenopods.
Chlamydomonas is a genus of green algae consisting of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as “snow algae”.
Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogeneses, and genetics.
Aquatic photosynthetic organisms, such as Chlamydomonas reinhardtii, can modulate their photosynthesis to acclimate to CO2-limiting stress by inducing a carbon-concentrating mechanism (CCM) that includes carbonic anhydrases (CAH) and inorganic carbon (Ci) transporters.
The carbon-concentrating mechanism (CCM) allows C. reinhardtii to optimize carbon acquisition for photosynthesis. The CCM function to facilitate CO2 assimilation, when inorganic carbon (Ci; CO2 and/or HCO3−) is limited. By active Ci uptake systems, internal Ci levels are increased and then carbonic anhydrase supplies sufficient CO2 to ribulose 1,5-bisphosphate carboxylase/oxygenase (“RuBisCO”) by the dehydration of accumulated bicarbonate.
In the present invention newly identified components of the CCM are integrated into higher plants in order to increase one or more of the characteristics selected from the group of photosynthetic rate, photosynthetic carbon fixation, chlorophyll level and/or biomass of subsequent plant generations, especially the T1 and/or T2 generation, and any further generation of said genetically modified higher plant.
By this modification the higher plant may not only grow better and become more competitive in known habitats, but may even thrive in climatic conditions traditionally not occupied by this plant.
Further examples for higher plants include cereals, legumes, fruits, roots and tubers, oil crops, fibre crops and trees.